In our three part series we have examined the use of biogas to reduce emissions and drawdown carbon as a tool to address climate change. We looked at some of the factors that make biogas suitable and some of the limitations that might make biogas less than optimal for a specific location or application in the first article, and biogas through the lens of the permaculture principles in the second article.
In this last article, we will examine some of the types of small scale biogas, and what applications they may be useful for. Included are links to the systems location and service or equipment providers.
There are three main kind of biogas digesters
1) Buried or sealed vault, popular in China, fairly expensive, requires skills to make, and takes time, but if built properly will last forever. These are primarily for animal based systems, especially pig and cattle manure.
2) Tank system, which functions like a vault, except the anaerobic conditions are created by the use of a sealed container of some kind. Water tanks and second hand Industrial Bulk Containers (IBC’s) are used for this. These are primarily food waste systems
3) Bag systems, which are very easy to make, very inexpensive, but relatively fragile (though there are exceptions to that, such as the Sistema Biobolsa, covered below). These are primarily animal waste systems.
4) Floating gas systems, which are easiest to make, but some have issues of a percentage of methane escaping to the atmosphere, which is counter productive to reduce the effects of climate change. Methane is much more powerful as a green house gas than carbon dioxide. Floating gas systems can be for food waste or for animal based systems, depending on size.
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